Reactivation of noble metal-containing zeolite catalyst materials

ABSTRACT

A process is described for rejuvenating a coke-deactivated noble metal-containing zeolite catalyst material which comprises sulfiding the deactivated catalyst material by contacting with a sulfiding agent such as hydrogen sulfide-containing gas, removing coke from the sulfided catalyst by contacting the catalyst with oxygen in the presence of sulfur dioxide, and thereafter reducing the catalyst in the presence of a reducing agent such as hydrogen. The process permits catalyst reactivation by burning off coke from the catalyst while avoiding excessive agglomeration of the noble metals thereon.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process of reactivating catalysts. Inparticular, it relates to the reactivation of noble metal-causingzeolite catalysts which have been deactivated by coke build-up.Catalysts which may be reactivated by the process of the presentinvention include those that have become deactivated during hydrocarbonhydroprocesses, such as the reforming or catalytic dewaxing ofhydrocarbon feedstocks.

2. Discussion of the Prior Art

Reactivation of platinum catalysts utilized in hydrocarbonhydroprocessing procedures such as reforming is known in the art.Processes which utilize chlorine and oxygen in catalyst reactivation areparticularly well-known. For example, U.S. Pat. No. 2,906,702 to Brennanet al discloses a method of restoring an alumina-supported platinumcatalyst after deactivation occurring during the reforming ofhydrocarbons. This method teaches contacting a deactivatedplatinum-alumina catalyst with a gaseous chlorine, fluorine, or otherhalogen or halogen-affording substance at an elevated temperature. U.S.Pat. No. 3,134,732 to Kearby et al teaches a method for reactivatingnoble metal catalyst supported on alumina by contacting the catalystwith halogen-containing gas, stripping excess halogen therefrom, andsubjecting the resulting catalyst to a reduction step with ahydrogen-containing gas. In this disclosure, the agglomerated metal ispresent on the surface of the alumina as small crystallites. It is alsoknown in the art to regenerate noble metal- and platinum groupmetal-containing zeolite catalysts. Regeneration of noble metal-loadedzeolite catalysts required certain procedural modifications to regainthe activity of the metal. U.S. Pat. No. 3,986,982 to Crowson et altreats deactivated platinum group metal-loaded zeolites by contactingthem with a stream of an inert gas containing from 0.5 to 20 percentvolume of free oxygen and from 5 to 500 ppm volume of chlorine aschlorine, HCl, or an organic chlorine-containing material. The resultingcatalyst is purged to remove residual oxygen and chlorine and thenreduced in a stream of hydrogen at 200° to 600° C.

The treatment of noble metal-containing catalyst material with sulfurcompounds is also known in the art. For example, U.S. Pat. No. 3,661,768to Davis, Jr., et al. describe a method of regenerating a bimetallicreforming catalyst such as platinum-rhenium on alumina which includescontacting the catalyst with hydrogen sulfide to convert platinum toplatinum sulfide. Prior to sulfiding, the catalyst is contacted withchlorine and steam in order to effect chlorination.

However, all of the above treatments require certain precautions owingto the corrosive nature of the halogens ued. In addition, certainhalogen materials employed in these processes add significantly to thecost of catalyst regeneration. In order to avoid the drawbacksassociated with halogen use, it would be advantageous to reactivatecatalysts in the absence of halogens. However, when deactivating cokepresent on a catalyst material is exposed to an oxidizing atmosphereconsisting of oxygen and an inert gas, such as nitrogen, substantiallyall of the noble metal present on the catalyst becomes catalyticallyinactive.

SUMMARY OF THE INVENTION

It has now been found that coke-deactivated noble metal-containingzeolite catalyst materials can be reactivated without significant lossof the metal function activity therein. In accordance with the presentinvention, a deactivated platinum group or noble metal-containingzeolite catalyst material is regenerated by a method which comprises:sulfiding the deactivated catalyst material by contacting it with asulfiding agent such as hydrogen sulfide in hydrogen under sulfidingconditions, removing deactivating coke by contacting the sulfidedcatalyst material with oxygen in the presence of sulfur dioxide underoxidizing conditions, and reducing the resulting catalyst material byexposure to a reducing agent such as hydrogen under reducing conditions.The catalyst treated in accordance with the present invention exhibitsenhanced activity owing to the burn-off of deactivating coke as well asretention of significant noble metal dispersion.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention relates to a process for regenerating an agednoble metal-containing zeolite catalyst material to provide a catalystmaterial of enhanced activity which retains a substantial portion of itsnoble metal in a dispersed form. The process comprises sulfiding theaged catalyst, oxidizing the coke on the sulfided catalyst material withoxygen in the presence of sulfur dioxide under suitable oxidizingconditions, and thereafter reducing the catalyst material by contactwith hydrogen under suitable reducing conditions.

Hydrogen sulfide is a suitable sulfiding agent for the purposes of thepresent invention. Preferably, the sulfiding agent is combined withhydrogen to form a mixture containing 0.1 to 10 volume percent hydrogensulfide, preferably about 1 to 2 volume percent hydrogen sulfide.Suitable conditions for sulfiding include temperatures of about 300° to500° C., preferably about 350° to 450° C., say about 400° C. Pressuresmay range from about 1 to 400 psig, preferably about 150 to 250 psig.Preferably, the deactivated catalyst material is exposed to theforegoing sulfiding conditions at least until "breakthrough" of thesulfiding agent is observed at the outlet of the sulfiding vessel, i.e.,the sulfiding agent is detected in the sulfiding vessel effluent.

The sulfided catalyst material is treated to burn off deactivating cokematerials under controlled oxidizing conditions at moderate temperaturesand oxygen concentrations. Suitable oxidizing conditions includetemperatures ranging from about 100° to 500° C., preferably about 400°to 450° C., pressures ranging from about 100 to 400 psig, preferablyabout 150 to 250 psig. It is preferred that the oxidizing conditions bemild enough to prevent any alteration in the crystal structure of thezeolite being treated. Sulfided catalyst material is contacted with agas stream containing oxygen as well as sulfur dioxide. Generally, thegas stream may contain about 1 to 10 volume percent oxygen and 100 ppmto 2 volume percent sulfur dioxide, preferably 1 to 3 volume percentoxygen and 0.05 to 1 volume percent sulfur dioxide. The presence ofsulfur dioxide prevents or reduces agglomeration of the noble metalsdispersed throughout the catalyst during the removal of coke from thezeolite catalyst material.

Dispersion of the noble metals can be measured by hydrogenchemisorption, e.g., Temperature Programmed Desorption (TPD) ofhydrogen. This technique can indicate the extent of noble metalagglomeration of a catalyst material. Details of this analyticaltechnique may be found in "The Stoichiometry of Hydrogen and COChemisorption of Ir/γ-Al₂ O₃ ", Vol. 78, Journal of Catalysis, pp.319-326, Krishnamurthy et al., (1982).

The reducing procedure which follows removal of the coke from thecatalyst material utilizes any suitable reducing agent, preferablyhydrogen. Reduction of the catalyst material is achieved by contactingit with the reducing agent under suitable reducing conditions. Theseinclude temperatures ranging from about 300° to 500° C., preferablyabout 350° to 450° C. and contact times ranging from about 2 to 10hours, preferably about 3 to 5 hours. Where the reducing agent is in thegaseous form, e.g., hydrogen, said reduction is carried out at pressuresranging from about 1 to 400 psig, preferably about 150 to 250 psig.

The zeolites which may be rejuvenated by the process of the presentinvention include large pore zeolites such as Zeolite Y, zeolite beta,ZSM-3, ZSM-4, ZSM-18 and ZSM-20, as well as zeolites having a constraintindex of about 1 to 12 and silica to alumina mole ratio greater thanabout 12. Examples of such materials include ZSM-5, ZSM-11, ZSM-5/ZSM-11intermediates, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similarmaterials.

Zeolite Y is described in greater detail in U.S. Pat. No. 3,130,007. Theentire description contained within this patent, particularly the X-raydiffraction pattern of therein disclosed Zeolite Y, is incorporatedherein by reference.

Zeolite beta is described in U.S. Pat. No. 3,308,069. That description,including the X-ray diffraction pattern of zeolite beta, is incorporatedherein by reference.

ZSM-3 is described in greater detail in U.S. Pat. No. 3,415,736. Thatdescription, and in particular the X-ray diffraction pattern of saidZSM-3, is incorporated herein by reference.

ZSM-4 is described in U.S. Pat. No. 4,021,447. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886 and Re.29,948. The entire descriptions contained within those patents,particularly the X-ray diffraction pattern of therein disclosed ZSM-5,are incorporated herein by reference.

ZSM-11 is described in greater detail in U.S. Pat. No. 3,709,979. Thatdescription, and in particular the X-ray diffraction pattern of saidZSM-11, is incorporated herein by reference.

ZSM-5/ZSM-11 intermediate compositions are described in U.S. Pat. No.4,229,424. That description, and in particular the X-ray diffractionpattern of said compositions disclosed therein, is incorporated hereinby reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-18 is described in U.S. Pat. No. 3,950,496. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-20 is described in U.S. Pat. No. 3,972,983. The entire contentthereof, particularly the specification of the X-ray diffraction patternof the disclosed zeolite, is incorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire contentthereof, particularly the specification of the X-ray diffraction patternof the disclosed zeolite, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of thatzeolite, and particularly the X-ray diffraction pattern thereof, isincorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that zeolite, and particularly the specified X-raydiffraction pattern thereof, is incorporated herein by reference.

ZSM-48 is more particularly described in U.S. Pat. No. 4,234,231, theentire contents of which is incorporated herein by reference.

Particularly preferred zeolites for the purposes of the presentinvention are those which have high silica-to-alumina mole ratios, e.g.greater than about 20 or even greater than 70 or 100.

The catalyst treated by the process of the present invention contains atleast one noble metal such as platinum, palladium, iridium, osmium,rhodium, rhenium and ruthenium in amounts ranging from about 0.1 to 5weight percent, preferably about 0.3 to 0.9 weight percent. These noblemetals are generally associated with and supported on a zeolitecatalyst. The process may also be used to regenerate multimetalliccatalysts which contain one of the above noble metals and another metalselected from Groups IB, IVB, VIIA, or VIII of the Periodic Table. Thezeolite catalyst treated can be binder free or it may contain aninorganic oxide binder such as alumina, silica, silica-alumina,magnesia, titania, zirconia, or thoria.

This invention will be better understood by reference to the followingexamples.

EXAMPLE 1

10 grams of a catalyst material of zeolite beta comprising, 35 wt.%alumina and 0.59 wt.% platinum was exposed to hydrocarbon conversionconditions resulting in a coke build-up thereon. The deactivatedcatalyst was regenerated by sulfiding to breakthrough with a mixture of2 volume percent H₂ S/98 volume percent H₂ at 400° C. The sulfidedcatalyst was then regenerated by exposure to a gas containing 96.3volume percent N₂, 3 volume percent O₂ and 0.7 volume percent SO₂ at400° to 450° C. for 0.5 hours in order to burn off the coke. Theresulting catalyst was measured by hydrogen chemisorption for platinumdispersion. The regenerated catalyst had a platinum dispersion of 0.33compared with a dispersion of 0.57 for fresh catalyst.

EXAMPLE 2

A 10 gm sample of the coked catalyst of Example 1 was regenerated bycontact with a mixture containing 97 volume percent N₂ and 3 volumepercent O₂ at 400° to 450° C. to achieve coke burn-off. The regeneratedcatalyst was thereafter reduced for one hour at 450° C. in hydrogen.Platinum dispersion as measured by hydrogen chemisorption was 0.

A comparison of Examples 1 and 2 indicates that the reactivation processof the present invention is effective in retaining a significant portionof the initial Pt dispersion of a catalyst which would otherwise be lostby conventional regeneration treatment.

It is claimed:
 1. A process for regenerating a coke-deactivated noblemetal-containing zeolite catalyst material containing about 0.1 to 5weight percent noble metal, which comprises: sulfiding said deactivatedcatalyst material by contact with a hydrogen sulfide-containing gas attemperatures ranging from about 300° C. to 500° C., pressures rangingfrom about 1 to 500 psig, in the presence of a hydrogen sulfide-hydrogenmixture containing about 0.1 to 10 volume percent hydrogen sulfide,removing coke from the sulfided catalyst by contacting said catalystwith oxygen in the presence of sulfur dioxide under oxidizingconditions, wherein said oxidizing conditions include temperaturesranging from about 100° to 500° C., pressures ranging from about 100 to400 psig, and exposure to a gas stream containing about 100 ppm to 2volume percent SO₂ and about 1 to 10 volume percent O₂, and exposing theresulting catalyst material to hydrogen under reducing conditionscomprising temperatures ranging from about 300° to 500° C., pressuresranging from about 100 to 400 psig, and contact times ranging from about2 to 10 hours.
 2. The process of claim 1 wherein said sulfidingtemperatures range from about 350° to 450° C., said sulfiding pressuresrange from about 150 to 250 psig and said mixture contains about 2volume percent hydrogen sulfide.
 3. The process of claim 1 wherein saidoxidizing temperatures range from about 400° to 450° C., and saidoxidizing gas stream contains about 0.05 to 1 volume percent sulfurdioxide and about 1 to 3 volume percent oxygen.
 4. The process of claim1 wherein said reducing temperatures range from about 350° to 450° C.,said reducing pressures range from about 150 to 250 psig, and saidreducing contact time ranges from about 3 to 5 hrs.
 5. The process ofclaim 1 wherein the framework silica to alumina mole ratio of saidzeolite is at least about
 20. 6. The process of claim 1 wherein theframework silica to alumina mole ratio of said zeolite is at least about70.
 7. The process of claim 1 wherein the framework silica to aluminamole ratio of said zeolite is at least about
 100. 8. The process ofclaim 1 wherein said catalyst material contains a zeolite having aconstraint index ranging from about 1 to 12 and a silica to alumina moleratio of at least about
 12. 9. The process of claim 1 wherein saidcatalyst material contains a zeolite selected from the group consistingof ZSM-5, ZSM-5/ZSM-11 intermediate, ZSM-11, ZSM-12, ZSM-22, ZSM-23,ZSM-35, ZSM-38 and ZSM-48.
 10. The process of claim 1 wherein saidcatalyst material contains a zeolite selected from the group consistingof zeolite beta, Zeolite Y, ZSM-3, ZSM-4, ZSM-18 and ZSM-20.
 11. Theprocess of claim 1 wherein said zeolite is zeolite beta.
 12. The processof claim 1 wherein said zeolite is ZSM-5.
 13. The process of claim 1wherein said zeolite contains a metal selected from the group consistingof platinum, palladium, iridium, osmium, rhodium, rhenium and ruthenium.14. The process of claim 13 wherein said zeolite catalyst contains about0.3 to 0.9 weight percent platinum group metal.
 15. The process of claim1 wherein said catalyst contains an inorganic oxide binder.
 16. Theprocess of claim 14 wherein said binder is selected from the groupconsisting of alumina, silica, silica-alumina, magnesia, titania,zirconia and thoria.
 17. The process of claim 14 wherein said binder isalumina.
 18. The process of claim 14 wherein said binder is silica. 19.The process of claim 14 wherein said binder is silica-alumina.